This invention relates to fuel delivery systems and particularly those for transmitting fuel oil to combustion equipment such as diesel cycle internal combustion engines, gas turbine devices, and furnaces.
At sufficiently low temperatures, all engines and other fuel oil fired devices using petroleum based distillate fuels suffer a common problem of paraffin and ice crystal formations which can lead to blockages of fuel flow, particularly at points of restriction such as sharp or right angle bends in the fuel supply conduits, at fuel filters and at fuel filter connection points. Fuels have characteristic temperatures at which they become "cloudy" with suspended wax particles and at which they "freeze" or become a semi-solid mass, referred to as their cloud and pour points, respectively. Some distillate fuels have a cloud point of 20 degrees Fahrenheit and a pour point of 0 degrees Fahrenheit. Clogging in fuel filters and lines is a serious problem and results in reduction or stoppage of fuel flow to the associated combustion apparatus.
A common practice has been to attempt to eliminate fuel system blockages by introducing solvents in the fuel or by heating the components of the fuel delivery system. Although these approaches are effective while the associated device is operating, they are ineffective during periods of idleness where prolonged cold soaking can occur. A major problem, therefore, facing users of fuel oil combustion devices is the cold soak which effectively creates paraffin formation throughout the fuel delivery system, including the conduits connecting the various components thereof. The standard method of eliminating these paraffin formations after cold soak has been to introduce a higher ambient temperature, either by using external heat sources, or by moving the device into a heated building. In order to prevent fuel clogging within the conduits and connections between the various components of a fuel delivery system, it would be necessary to apply external heat to each of these components. Such approach would be inefficient from an energy input standpoint and would further likely not provide the rapid start-up capability which is desired in many applications.
While operating in high ambient temperature environments, distillate fuels can partially vaporize and dissolved gases may precipitate out of solution thereby creating entrapped gas pockets within the fuel delivery circuit. The likelihood of such vapor formations becomes particularly likely in high altitude conditions. This condition, often refered to as vapor lock, creates problems particularly for diesel engines since their fuel injection pumps are not designed to pump gases.
In view of the above, it is an object of this invention to provide a fuel delivery system which provides protection from fuel conduit and fitting restrictions without the requirement of external heat being applied to each of these components. It is a further object of this invention to provide a fuel delivery system capable of delivering warmed fuel to an engine or other combustion device with a minimal warm-up time period. It is another object to provide a fuel delivery circuit which provides protection from fuel line vapor lock. It is yet another object to provide such a system which is inexpensive to provide and simple in operation.
The above objects of this invention are achieved by providing a fuel delivery system having fuel lines which are purged of fuel when the associated device is shut down and reprimed prior to operation to eliminate entrained gases. By purging the fuel conducting conduits of the system, formation of a solidified "plug" of fuel in the lines cannot develop. Prior to start-up of the combustion device, a quantity of fuel is heated and then pumped into the circuit in a liquid state. This invention therefore eliminates the problems associated with fuel solidification occurring in fuel lines during periods of nonuse. The application of this concept is believed to be capable of resulting in a system which is entirely self-sufficient in providing fuel for satisfactory engine start-up and operation even after prolonged periods of exposure to temperatures down to -65 degrees Fahrenheit, when distillant fuels are utilized which become a solid at temperatures well above that temperature. In addition to providing protection from cold weather fuel solidification, several embodiments of this invention provide a return path for gases entrapped within the fuel lines thereby eliminating vapor lock problems when operating in high ambient temperatures.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.